Fish oils are major sources of nutritionally valuable compounds, such as the polyunsaturated fatty acids ω-3 EPA and DHA. Nevertheless, many commercially available fish oils contain substantial amounts of pollutants, generally referred to as Persistent Organic Pollutants (POPs), which are organic chemical compounds that are lipophilic and environmentally persistent in that they accumulate through the food chain in fat tissue and oils of marine organisms, including marine mammals. The toxicity and biomagnification of POPs in the marine environment is well characterized.
According to the Stockholm Convention, POPs include organochlorinated pesticides such as Aldrin, Dieldrin, Chlordane, DDT, Endrin, Heptachlor, Mirex, Toxaphene, industrial chemicals such as polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), and dibenzodioxins and dibenzofurans which are by-products of several industrial chemical processes. In addition to POPs, there are other potentially toxic pollutants that persist in the environment but are not listed as POPs by the Stockholm Convention. These pollutants are referred to as Persistent Toxic Substances (PTSs) and include polycyclic aromatic hydrocarbons (PAHs), phthalate esters, polybrominated diphenyl ethers (PBDEs) used as flame retardants, polychlorinated naphthalenes (PCNs), bisphenol A (BPA), alkylphenols, and metals such as mercury, cadmium, lead, and arsenic. It is common for many crude and refined fish oils to contain dozens of pollutant organic compounds between the various types of POPs, PTSs, and their congeners.
In order to use fish oil as a source of EPA and DHA or for the production of EPA and DHA concentrates for nutraceutical and pharmaceutical purposes, it is necessary to reduce the levels of POPs and PTSs in the fish oil to at least the maximum levels permitted by existing regulations without altering the levels of nutritionally valuable compounds or affecting the oxidative stability of the oil. Processes for decreasing the levels of organic pollutants in fish oil have previously been disclosed. These processes include adsorption processes with activated carbon, steam stripping, and vacuum distillation with or without a carrier fluid. However, the amount and great variety of pollutants that may be present in the raw fish oil presents a significant challenge.
U.S. Pat. No. 6,469,187, for example, discloses a process to obtain marine oil with reduced amounts of polychlorinated dioxins, furans, biphenyls and polycyclic aromatic hydrocarbons by using activated carbon. Most marine oils, however, also contain many other types of pollutants, among them flame retardants (PBDEs) and chlorinated pesticides such as chlorinated hydrocarbons and chlorinated camphenes (toxaphenes), and the active carbon absorption type process disclosed in U.S. Pat. No. 6,469,187 is known to have little to practically no effect on reducing PBDEs.
Vacuum distillation processes for decreasing the amount of environmental pollutants are also known. This type of process typically includes adding a carrier fluid or volatile working fluid to the polluted oil and then subjecting the mixture to vacuum distillation. Numerous processes for the production of polyunsaturated fatty acid ethyl esters concentrates from fish oil are known, resulting in a variety of ethyl ester by-products or distilled fractions of different composition. EP 1523541 B1, for example, discloses a vacuum distillation process in which the carrier fluid is a fatty acid ethyl ester mixture generated as a by-product or distilled fraction from the production of polyunsaturated fatty acid ethyl ester concentrates from fish oil. The carrier fluid is the lighter fraction resulting from the distillation of fish oil transesterified with ethyl alcohol and includes C14 or C16 fatty acids and C18 fatty acids. This lighter fraction typically includes not more than 50% of unsaturated fatty acids esters.
Numerous processes for the production of polyunsaturated fatty acid ethyl esters concentrates from fish oil are known, resulting in a variety of ethyl ester by-products or distilled fractions of different composition. In addition, different compositions of fatty acid ethyl esters can be formulated from commercially available individual fatty acid esters or from ethyl esters prepared by using free fatty acids and ethylating said fatty acids. The formulation of ester mixtures from individual esters has the advantage of not being restricted to mixtures of compositions predetermined by the nature of the source oil.
Nevertheless, because fish oils may contain dozen of different pollutants, choosing an efficient carrier fluid for the removal of POPs through vacuum distillation of fish oils is challenging and complicated by (1) the variation in solubility and lipolificity of the several different POPs in the carrier fluid and (2) the broad spectrum of vapor pressures of those same components. For example, between PCBs congeners there is a vapor pressure variation of 8 orders of magnitude at room temperature (between 10−12 to 10−4 mmHg) and the selection of an efficient carrier fluid is further complicated because their vapor pressures and respective solubilities at higher temperatures, such as the operating temperatures of distillation columns, are unknown. Something similar happens with the others types of POPs and PTSs. Therefore, a carrier fluid composition that is suitable for use in vacuum distillation processes and capable of reducing the concentration of a wide variety of POPs and PTSs in fish oil to acceptable levels in an economically efficient process would be desirable.